Depression is a clinical disorder that may begin at any age, although it usually begins in the mid-20s and 30s. The Diagnostic and Statistical Manual-IV (DSM-IV) criteria used to diagnose depression are provided in Table 1. These symptoms may develop over days to weeks. Some people have only a single episode, with a full return to premorbid function. However, more than 50 percent of those who initially suffer a single major depressive episode eventually develop another.
The point prevalence for major depressive disorder in the Western industrialized nations is 2.3 to 3.2 percent for men and 4.5 to 9.3 percent for women. The lifetime risk for major depressive disorder is 7 to 12 percent for men and 20 to 25 percent for women. Risk factors for major depressive disorder include female gender (especially during the postpartum period), a history of depressive illness in first-degree relatives and prior episodes of major depression. Patients with major depressive disorder have substantial amounts of physical and psychological disability, as well as occupational difficulties. Untreated major depressive disorder has a substantial effect on health and functioning. Physical complaints are also common during a major depressive episode.
Although a genetic component has been suggested in depression, it has not been confirmed, much less characterized (U.S. Department of Health and Human Services; AHCPR Publication No. 93-0550, 1993). Further, it has not been reported whether the genetic bases and corresponding biochemical mechanisms underlying the different forms of depression are different in kind or only in degree. At present no specific genetic or biochemical tests are available for the positive diagnosis of depression. Diagnosis and treatment is presently based solely on patient self-reporting and symptom description. The clinical heterogeneity associated with depression has complicated patient reporting as well as the diagnosis and treatment of the disorder. As a result, no clear modality of treatment for all individuals with depression has emerged, and treatment as well as diagnosis varies greatly not only from patient to patient but from physician to physician. Thus, many sufferers of depression are not diagnosed or not effectively treated.
Identification of inheritance pattern(s) and genetic bases for depression would greatly facilitate the diagnosis and treatment of this disorder. The present invention fulfills this and other needs by mapping a gene associated with an increase in susceptibility to depression to a region within chromosome 19.